In textile thread processing machines, such as two-for-one twisters, thread is pulled from a hollow supply package or packages carried by a stationary carrier mechanism in each of a plurality of spindle assemblies and passed through the hollow center of the supply package and the spindle assembly by directing the thread into the upper end of a thread entry tube and through a yarn passageway in the spindle assembly. During processing of thread in such a spindle assembly of a thread procssing machine, it is often desirable to provide a thread brake through which the thread passes in its travel through the spindle assembly for applying additional tension to the thread being processed.
Various constructions of thread brakes suitable for use in spindle assemblies of textile yarn processing machines have heretofore been proposed. However, these previously proposed thread brake mechanisms were not entirely suitable for use with two independent individual threads which may be fed into the spindle assembly at varying tensions, which is often done in various yarn processing operations, for applying respective braking forces to the individual threads depending upon the respective feeding tensions thereof.
An example of such a thread brake mechanism is shown in German Patent DE-PS No. 857 166. In this thread brake mechanism, the brake body rests flat on the surface of the braking ring which has a central aperture and is limited radially in its movement. Upon a rise in the tension of thread being fed through such brake mechanism, the brake body is pushed by the thread being fed between the brake body and the braking ring to such an extent that it abutts against the inner wall of the brake housing and is then raised on one side. This one-sided raising of the brake body leads to a lower loading of the thread and thus to a reduction in the overall braking load. Accordingly, this known thread brake mechanism is only suitable for cases where either an individual thread or else an already plied thread is fed through the brake mechanism to the spindle assembly. If two independent individual threads are fed through this known thread brake mechanism, the brake body of such thread brake mechanism would respond to the tension level of the one or of the other thread and the brake body would display an indifferent behavior with respect to the other thread.
A further example of previously known thread brake mechanisms is disclosed in U.S. Pat. No. 4,287,712, assigned to the assignee of the present application. The brake mechanism of this patent includes a brake body designed as a sphere which is seated in a braking ring having a conical shape on its upper side. This thread brake mechanism is also not suitable for use with two independent individual threads being fed therethrough at varying tensions. It has been shown that, in the case of this known thread brake mechanism, when two threads at varying tension are fed through, the thread with the greater tension remains between the brake body and the braking ring and experiences a still higher tension. On the other hand, the thread being fed therethrough with less tension, which also has a tendency for a loop forming, is tautened in accordance with the level of the braking force produced by the spherical brake body. Its greater length, which it has as a result of the slacker feeding tension, is stripped out only in the direction of the thread afflux. The surplus thread length can only again with subsequent tauter thread portions form the length compensation. This procedure is thus subject to accidents.